Chemical-mechanical polishing (“CMP”) processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, Field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
In a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains a chemical that interacts with or dissolves portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The carrier also can oscillate across the polishing pad on the polishing table.
Polishing pads used in chemical-mechanical polishing processes are manufactured using both soft and rigid pad materials, which include polymer-impregnated fabrics, microporous films, cellular polymer foams, non-porous polymer sheets, and sintered thermoplastic particles.
A pad containing a polyurethane resin impregnated into a polyester non-woven fabric is illustrative of a polymer-impregnated fabric polishing pad. Microporous polishing pads include microporous urethane films coated onto a base material, which is often an impregnated fabric pad. These polishing pads are closed cell, porous films. Cellular polymer foam polishing pads contain a closed cell structure that is randomly and uniformly distributed in all three dimensions.
Non-porous polymer sheet polishing pads include a polishing surface made from solid polymer sheets, which have no intrinsic ability to transport slurry particles (see, for example, U.S. Pat. No. 5,489,233). These solid polishing pads are externally modified with large and/or small grooves that are cut into the surface of the pad purportedly to provide channels for the passage of slurry during chemical-mechanical polishing. Such a non-porous polymer polishing pad is disclosed in U.S. Pat. No. 6,203,407, wherein the polishing surface of the polishing pad comprises grooves that are oriented in such a way that purportedly improves selectivity in the chemical-mechanical polishing.
Also in a similar fashion, U.S. Pat. Nos. 6,022,268, 6,217,434, and 6,287,185 disclose hydrophilic polishing pads with no intrinsic ability to absorb or transport slurry particles. The polishing surface purportedly has a random surface topography including (a) microaspersities that have a dimension of 10 μm or less and are formed by solidifying the polishing surface and (b) macro defects (or macrotexture) that have a dimension of 25 μm or greater and are formed by cutting.
Sintered polishing pads comprising a porous open-celled structure can be prepared from thermoplastic polymer resins. For example, U.S. Pat. Nos. 6,062,968 and 6,126,532 disclose polishing pads with open-celled, microporous substrates, produced by sintering thermoplastic resins. The resulting polishing pads preferably have a void volume of 25-50% and a density of 0.7-0.9 g/cm3. Similarly, U.S. Pat. Nos. 6,017,265, 6,106,754, and 6,231,434 disclose polishing pads with uniform, continuously interconnected pore structures, produced by sintering thermoplastic polymers at high pressures in excess of 689.5 kPa (100 psi) in a mold having the desired final pad dimensions.
Polishing pads having a microporous foam structure are commonly known in the art. For example, U.S. Pat. No. 6,454,634 discloses a porous polishing pad having a hydrolytically stable layer and optionally comprising abrasive particles. Similarly U.S. Pat. No. 7,195,544 discloses a pad comprising a polymeric material having pores and a component dispersed within the pores. U.S. Patent Application Publication 2006/0046622 discloses a polishing pad comprising a porous polymeric material comprising two or more adjacent regions having non-zero void volumes.
Although several of the above-described polishing pads are suitable for their intended purpose, a need remains for other polishing pads that provide effective planarization, particularly in the chemical-mechanical polishing of a substrate. In addition, there is a need for polishing pads having satisfactory features such as polishing efficiency, low defectivity, and polishing uniformity. The invention provides such a polishing pad. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.